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authorBrian Foster <bfoster@redhat.com>2022-11-30 08:41:01 -0800
committerDarrick J. Wong <djwong@kernel.org>2022-11-30 08:41:01 -0800
commita79168a0c00d710420c1758f6c38df89e12f0763 (patch)
treef9a7d9faade51d699ff87f3aed8bf281ab19785b
parentf0c4d9fc9cc9462659728d168387191387e903cc (diff)
fs/remap_range: avoid spurious writeback on zero length request
generic_remap_checks() can reduce the effective request length (i.e., after the reflink extend to EOF case is handled) down to zero. If this occurs, __generic_remap_file_range_prep() proceeds through dio serialization, file mapping flush calls, and may invoke file_modified() before returning back to the filesystem caller, all of which immediately check for len == 0 and return. While this is mostly harmless, it is spurious and not completely without side effect. A filemap write call can submit I/O (but not wait on it) when the specified end byte precedes the start but happens to land on the same aligned page boundary, which can occur from __generic_remap_file_range_prep() when len is 0. The dedupe path already has a len == 0 check to break out before doing range comparisons. Lift this check a bit earlier in the function to cover the general case of len == 0 and avoid the unnecessary work. While here, account for the case where generic_remap_check_len() may also reduce length to zero. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
-rw-r--r--fs/remap_range.c7
1 files changed, 2 insertions, 5 deletions
diff --git a/fs/remap_range.c b/fs/remap_range.c
index 654912d06862..8741ecd616a7 100644
--- a/fs/remap_range.c
+++ b/fs/remap_range.c
@@ -304,7 +304,7 @@ __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
/* Check that we don't violate system file offset limits. */
ret = generic_remap_checks(file_in, pos_in, file_out, pos_out, len,
remap_flags);
- if (ret)
+ if (ret || *len == 0)
return ret;
/* Wait for the completion of any pending IOs on both files */
@@ -328,9 +328,6 @@ __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
if (remap_flags & REMAP_FILE_DEDUP) {
bool is_same = false;
- if (*len == 0)
- return 0;
-
if (!IS_DAX(inode_in))
ret = vfs_dedupe_file_range_compare(file_in, pos_in,
file_out, pos_out, *len, &is_same);
@@ -348,7 +345,7 @@ __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
ret = generic_remap_check_len(inode_in, inode_out, pos_out, len,
remap_flags);
- if (ret)
+ if (ret || *len == 0)
return ret;
/* If can't alter the file contents, we're done. */